The present invention relates to a charge indicating system which is capable of indicating an interruption in the power generation of a charging generator, when that interruption is caused by the disconnection of an energizing circuit or the like, by generating a voltage difference between a rectified output terminal and a storage battery and by detecting this voltage difference. The subject matter of this application is related to that of copending U.S. application Ser. No. 477,802 and 478,000, filed by the present applicants and commonly assigned.
A system according to the prior art will first be described with reference to FIG. 1. In this figure, reference numeral 1 indicates a three-phase alternating-current generator which is mounted on a vehicle (not shown) or the like and is driven by a engine (not shown). The generator 1 is constructed of three-phase star-connected armature coils 101 and a field coil 102. Numeral 2 indicates a full-wave rectifier for rectifying the a.c. output of the aforementioned generator 1. The rectifier 2 includes first and second rectified output terminals 201 and 202 and a ground terminal 203. Numeral 3 indicates a voltage regulator which is made operative to control the output voltage of the aforementioned generator to a first predetermined value by controlling the field current flowing through the aforementioned field coil 102.
In the regulator 3, numeral 301 indicates a surge absorbing diode connected with both ends of the aforementioned field coil 102. Numerals 302 and 303 indicate Darlington-connected power transistors for interrupting the current to be supplied to the aforementioned field coil 102. Numeral 304 indicates a resistor which constitutes the base circuit of the transistors 302 and 303. Numeral 305 indicates a control transistor for turning the aforementioned transistors 302 and 303 on and off. Numeral 306 indicates a Zener diode for detecting the voltage of the second rectified output terminal 202 of the aforementioned rectifier, and rendered conductive when the output voltage detected reaches the first predetermined value. Numerals 307 and 308 indicate resistors connected in series with each other to construct a voltage dividing circuit. Numeral 309 indicates an initial coil energization resistor connected in parallel with a charge indicating lamp 6, for supplying an initial energization current to the aforementioned generator 1 even if the indicating lamp 6 is disconnected. Numerals 4 and 5 indicate a storage battery and a key switch, respectively.
The operation of the prior art system thus constructed will now be described. When the key switch 5 is closed to start the engine, the transistors 302 and 303 are supplied with base current from the battery 4 through the key switch 5 and the resistor 304 so that they are rendered conductive. When the transistors 302 and 303 become conductive, the battery 4 supplies field current to the field coil 102 through the key switch 5, the charge indicating lamp 6, the resistor 309, the field coil 102 and transistors 302 and 303 so that a field magnetomotive force is generated.
When the engine is started in this state so that the generator 1 is driven, an a.c. output is induced in the armature coils 101 in accordance with the engine r.p.m. and is full-wave rectified by the full-wave rectifier 2. At this time, the rectified output is lower than the first predetermined value and the voltage at the voltage driving point of the voltage driving circuit, which is constructed of the resistors 307 and 308, is still low. As a result, the Zener diode 306 is not yet conductive but maintains its nonconductive state so that the supply of field current is maintained. As a result, the output voltage of the generator 1 is raised in accordance with the rise in generator r.p.m.
When this r.p.m. is increased such that the output voltage exceeds the aforementioned first predetermined value, the potential at the dividing point of the aforementioned voltage driving circuit is also increased to render the Zener diode 306 conductive, through which base current is supplied to the transistor 305 so that this transistor 305 is rendered conductive. When the transistor 305 becomes conductive, the transistors 302 and 302 are disconnected to interrupt the current flowing through the field coil 102, so that the output voltage of the generator 1 drops.
When the output voltage has fallen to the first predetermined value, the Zener diode 306 and the transistor 305 are rendered nonconductive, and the transistors 302 and 303 are rendered conductive to energize the field coil 102, so that the output voltage of the generator 1 is again raised.
By repeating the operations thus far described, the output voltage of the generator 1 is controlled to the aforementioned predetermined value so that the battery 4 is charged with the controlled voltage. At this time, on the other hand, the output voltage of the second rectifier output terminal 202 reaches the first predetermined value so that there is no potential difference between it and the battery 4. As a result, the charge indicating lamp 6 is turned off to indicate the charged state of the battery 4.
In the prior art system thus far described, however, if the coil energizing circuit is partially disconnected, the charge indicating lamp 6 is not lit even when the generator 1 generates no output power. This creates a defect in that this state is not detected, to invite the full discharge of the battery.